Laminate flooring usually consists of a core of a 6-9 mm fibreboard, a 0.2-0.8 mm thick upper decorative surface layer of laminate and a 0.1-0.6 mm thick lower balancing layer of laminate, plastic, paper or like material. The surface layer provides appearance and durability to the floorboards. The core provides stability, and the balancing layer keeps the board plane when the relative humidity (RH) varies during the year. Laminate flooring can also be made of compact laminate. Surface layer and balancing layer are then applied to a core of phenol-impregnated kraft paper or phenol-impregnated wood fibres. Manufacture of surface layer, core and balancing layer takes place while pressure and heat are being supplied. The floorboards are usually laid floating, i.e. without gluing, on an existing subfloor which does not have to be completely smooth or plane. Any irregularities are eliminated wholly or partly by means of base material in the form of e.g. board or foam which is placed between the floorboards and the subfloor. Traditional hard floorboards in floating flooring of this type are usually joined by means of glued tongue-and-groove joints (i.e. joints involving a tongue on one floorboard and a tongue groove on an adjoining floorboard) on long side and short side. When laying the floor, the boards are brought together horizontally, whereby a projecting tongue along the joint edge of one board is introduced into a tongue groove along the joint edge of an adjoining board. The same method is used on the long side as well as on the short side.
In addition to such traditional floors, which are joined by means of glued tongue-and-groove joints, floorboards have recently been developed which do not require the use of glue and instead are joined mechanically by means of so-called mechanical joint systems. These systems comprise locking means which lock the boards horizontally and/or vertically. The mechanical joint systems can be formed by machining of the core of the board. Alternatively, parts of the locking system can be formed of a separate material, which is integrated with the floorboard, i.e. joined with the floorboard even in connection with the manufacture thereof. Separate materials can either be fixedly secured to the floorboard mechanically, by means of glue and the like. They can also be mechanically secured in such a manner that they can, for instance, be displaced along the joint edge or be detached by an angular motion.
The main advantages of floating floors with mechanical joint systems are that they can easily and quickly by laid by various combinations of inward angling, snapping-in and displacement along the joint edge. Snapping-in can take place by displacement of the joint edges horizontally, vertically or at different angles. The floorboards can also easily be taken up again and used once more at a different location. A further advantage of the mechanical joint systems is that the edge portions of the floorboards can be made of materials which need not have good gluing properties.
The most common core material is a fibreboard with high density and good stability usually called HDF—High Density Fibreboard. Sometimes also MDF—Medium Density Fibreboard—is used as core. As a rule, these core materials are of high quality and often have an attractive surface which can resist penetration of moisture.
Thick surface layers of wood, for instance 1-4 mm, are usually applied to a core consisting of wood blocks whose fibre direction is perpendicular to the fibre direction of the surface layer. Particle board, fibreboard or plywood are also used both when the surface layer is thick and also when the surface layers are thin veneer with a thickness of e.g. 0.2-1.0 mm.
Laminate flooring and also many other floorings with a surface layer of plastic, wood, veneer, cork and the like are made by the surface layer and the balancing layer being applied to a core material. This application may take place by gluing a previously manufactured decorative layer, for instance when the fibreboard is provided with a decorative high pressure laminate which is made in a separate operation where a plurality of impregnated sheets of paper are compressed under high pressure and at a high temperature. The currently most common method when making laminate flooring, however, is direct laminating which is based on a more modern principle where both manufacture of the decorative laminate layer and the fastening to the fibreboard take place in one and the same manufacturing step. Impregnated sheets of paper are applied directly to the board and pressed together under pressure and heat without any gluing.
In addition to these two methods, a number of other methods are used to provide the core with a surface layer. A decorative pattern can be printed on the surface of the core, which is then, for example, coated with a wear layer. The core can also be provided with a surface layer of wood, veneer, decorative paper or plastic sheeting, and these materials can then be coated with a wear layer.
As a rule, the above methods result in a floor element in the form of a large board which is then sawn into, for instance, some ten floor panels, which are then machined to floorboards. The above methods can in some cases result in completed floor panels and sawing is then not necessary before the machining to completed floorboards is carried out. Manufacture of individual floor panels usually takes place when the panels have a surface layer of wood or veneer.
In all cases, the above floor panels are individually machined along their edges to floorboards. The machining of the edges is carried out in advanced milling machines where the floor panel is exactly positioned between one or more chains and bands mounted, so that the floor panel can be moved at high speed and with great accuracy past a number of milling motors, which are provided with diamond cutting tools or metal cutting tools, which machine the edge of the floor panel. By using several milling motors operating at different angles, advanced joint geometries can be formed at speeds exceeding 100 m/min and with an accuracy of ±0.02 mm.
Definition of Some Terms
In the following text, the visible surface of the installed floorboard is called “front side”, while the opposite side of the floorboard, facing the subfloor, is called “rear side”. The sheet-shaped starting material that is used is called “core”. When the core is coated with a surface layer closest to the front side and preferably also a balancing layer closest to the rear side, it forms a semi-manufacture which is called “floor panel” or “floor element” in the case where the semi-manufacture, in a subsequent operation, is divided into a plurality of floor panels mentioned above. When the floor panels are machined along their edges so as to obtain their final shape with the joint system, they are called “floorboards”. By “surface layer” are meant all layers applied to the core closest to the front side and covering preferably the entire front side of the floorboard. By “decorative surface layer” is meant a layer which is mainly intended to give the floor its decorative appearance. “Wear layer” relates to a layer which is mainly adapted to improve the durability of the front side. In a laminate floor, this wear layer often consists of a transparent paper containing melamine and aluminium oxide. By “reinforcing layer” is meant a layer which is mainly intended to improve the capability of the surface layer of resisting impact and pressure and, in some cases, compensating for the irregularities of the core so that these will not be visible at the surface. In high pressure laminates, this reinforcing layer usually consists of brown kraft paper which is impregnated with phenol resin. By “decorative layer” is meant a layer which is applied to the reinforcing layer in an analog manner, i.e. under the decorative surface layer, but with a view to achieving a predetermined appearance, rather than a reinforcing effect. The decorative layer can be identical with the reinforcing layer by this being stained or modified in some other manner to obtain a desired appearance.
By “the part of the core which is closest to the surface layer” is generally meant the part of the core which is positioned above the vertical locking means, and preferably at a shorter distance from the surface layer of the core than from the vertical locking means.
Regarding “plywood”, which consists of several layers of crosswise joined layers of wood, the inner layers of the plywood are to be considered to constitute a core, the outer layers being considered to constitute surface layer, reinforcing layer and/or decorative layer, according to the definitions above.
By “horizontal plane” is meant a plane which is parallel to the outer part of the surface layer. In the joined position, the two juxtaposed upper joint edges define a “vertical joint plane”.
The outer parts of the floorboard at the edge of the floorboard between the front side and the rear side are called “joint edge”. As a rule, the joint edge has several “joint surfaces” which can be vertical, horizontal, angled, rounded, bevelled etc. These joint surfaces can be made of different materials, for instance laminate, fibreboard, wood, plastic, metal (e.g. aluminium) or sealing material. By “joint edge portion” are meant the joint edge of the floorboard and part of the floorboard portions closest to the joint edge. By “decorative joint portion” is generally meant part of the surface of the floorboard which is intended to resemble a visible joint between, for instance, stone or wood material.
By “joint” or “joint system” are meant coacting connecting means which connect the floorboards vertically and/or horizontally. In connection with joining of the floorboards, “vertical” means a direction which is perpendicular to the horizontal plane. “Horizontal” means a direction which is perpendicular to the vertical joint plane of the respective joints.
The above techniques can be used to manufacture laminate floorings which are highly natural copies of wooden flooring. In recent years, imitations of stones, tiles and the like have become more and more common. In this context, it is tried to manufacture decorative joint portions between stones and tiles which should be as natural as possible. They should have decoration and structure other than those of the stone material and should also be somewhat lowered under the horizontal plane to resemble an embedded joint between two stones or tiles. The techniques used to manufacture these decorative joint portions are expensive and do not provide a natural appearance. It should be possible to increase the market for these types of flooring significantly if decorative joint edge portions could be made in a simpler and less expensive manner and with a more natural appearance.